1. Technical Field
The present invention pertains to an image display apparatus, and an image display method carried out in the image display apparatus, and particularly, relates to an image display apparatus which, on the basis of image data, applies a prescribed image display voltage between a pair of electrodes, at least one of which is composed of a transparent electrode, thereby moving particles enclosed between the electrodes to carry out image display by the particles arranged on the transparent electrode side, and an image display method in the image display apparatus.
2. Description of the Related Art
Conventionally, an image display apparatus has been proposed in which, particles colored, for example, black are enclosed, between two substrates at least one of which is transparent, and which are opposed to each other with a prescribed spacing, and the particles are friction-charged, whereby the particles between the substrates are moved to display an image.
At the initial stage of the period of use of the image display apparatus, the particles can be friction-charged by stirring by applying a vibration from the outside, causing particle movement by voltage application, applying a charge from the outside, or the like, to bring the particles into a prescribed charged state.
However, in an image display apparatus having a configuration as described above, repetition of display over a long period of time, continuous operation for many hours, and an environmental change (a change in temperature, humidity, or atmospheric pressure) lowers the electric-chargeability possessed by the particles, resulting in the quantity of charge being decreased. In such a situation, there arises a problem in that application of a predetermined image display voltage alone will not provide a sufficient display contrast, resulting in the display function being degraded.
In addition, if the quantity of charge of the particles is reduced, movement of the particles becomes difficult, which may result in a display defect being produced. Further, there may occur a state in which the number of particles which do not contribute to the display is increased, resulting from adherence of particles to the partition wall in the substrate, aggregation of particles, and the like. In such a case as well, there arises a problem in that a sufficient display contrast cannot be obtained.
In order to eliminate the above-mentioned problems, application of an alternating voltage has been proposed in order to achieve purposes, such as causing the particles to rub against one another to apply charges to them, vibrating the aggregated particles to separate them and return them to the individually movable state, and the like. For example, in Japanese Patent Application Laid-Open No. 2003-5277, a technique which renders the particles uniform by applying an alternating voltage, which is different from the image display voltage, to the particles dropping in the direction of gravity is described.
However, experiments have revealed that, depending upon the application conditions (such as the timing of application, the application time period, and the like), the quantity of charge of the particles may not be restored, and can be expected that there will be case where, even if the above-mentioned conventional art is used, the display quality which has been degraded by repetition of display, an environmental change, or the like, may not be restored to a state which is equivalent to that at the initial stage in the period of use.
In addition, in a case where the image display voltage which was set at the initial stage in the period of use no longer moves the particles, and a high voltage is applied as the image display voltage, an overcharge is then caused, resulting in even the pixels for which no write is to be performed being influenced by the application of the image display voltage. Due to this influence, a problem is caused such as in that, when black is to be displayed on the white background, for example, fogging occurs on the white background. In addition, application of too high a voltage presents a problem in that the service life of the image display apparatus itself is shortened.